[moshspeggeti]

However I don't know where the line is drawn between clever bartering and sharking here, so I've never been inclined to try it. Especially because I'm not bartering with an incorporated drone but a real person.

I would say the line is drawn is if you trade a significantly low amount, for a hat of significant value. I mean, if you go looking for noobs with Unusuals to rip them of their valuables for a very low amount, that is sharking. Usually when you barter with someone on TF2 outpost or a Trade server, they know the values of their hats and won't let them go that cheap, even if you lowball them it's usually no where as low as how much a shark would pay for an expensive hat.